1. Field of the Invention.
The invention relates generally to a protective cable coupling assembly for use with such as surface readout oil well tools and, more particularly, but not by way of limitation, it relates to an improved coupling structure that provides a controlled first weak point where the cable support will shear and a second weak point which will allow tool recovery.
2. Description of the Prior Art.
Applicant is unaware of any prior teachings that relate to a form of controlled weak point that allows surface readout oil well work to be performed with a greater degree of safety. Surface readout service has implicitly involved the necessity for working under pressure at the mouth of a well and, for this reason, it was necessary to use the thinnest possible cable. In those fields where combinations of depth, pressure and important production were found, the balance between diameter of cable and mechanical resistance to the needed stress was usually so precarious that the work could not, for all practical purposes, be performed with an acceptable margin of safety.
In prior practice, when a cable became hung within a well, its greatest stress was at the surface. Thus, if the testing tool could not be unhooked, it was necessary to stress the cable on the surface until some weak point allowed separation at the lower end of the cable. If the depth was great, the useful limit of the stress tension of the cable, less the weight of the vertical section of the cable (maximum pull-out), leave a very narrow margin for the construction of any "weak point". Keeping in mind that during operation the greater part of the capacity of the "weak point" is to carry the weight of the testing tool, which consists of the sinker bars plus the surface readout tool, and to open the sleeve of the E valve; we then find that the tolerance is so narrow that cutting can be effected through accidental maneuvers or even under the load produced by friction on the cable when flow velocity and production is high.
Due to the fact that the consequences of these types of accident were very costly, it was the practice of some operators to construct the clamp from the strongest cable, and when they could not unhook the surface readout tool, they were forced to cut the cable at the surface. Such failures discredited the surface readout operation in some oil fields to such a degree that revival of the practice now is extremely difficult.